Osteomalacia
Summary
Osteomalacia is a metabolic bone disease characterised by defective mineralisation of the osteoid matrix in adults. (In children with open growth plates, the same process causes Rickets). The hallmark is "soft bones" due to a lack of Calcium and Phosphate availability, most commonly caused by Severe Vitamin D Deficiency. Clinically, it presents with diffuse bone pain and proximal myopathy (waddling gait). Biochemically, it is defined by High ALP, Low/Normal Calcium, and Low Phosphate. [1,2]
Clinical Pearls
Osteomalacia vs Osteoporosis: This is the classic exam distinction.
- Osteoporosis: "Brittle bones". Mineralisation is normal, but the total mass is low. Blood tests are NORMAL. Painless until fracture.
- Osteomalacia: "Soft bones". Mineralisation is defective. ALP is HIGH. Painful (bone ache).
The "Waddle": Vitamin D receptors are abundant in muscle as well as bone. Severe deficiency causes a prominent Proximal Myopathy. Patients struggle to get out of a chair or climb stairs, walking with a waddling gait. This often leads to a misdiagnosis of neurological or rheumatological disease.
Pseudofractures (Looser's Zones): The pathognomonic X-ray sign. These are radiolucent bands perpendicular to the cortex, representing unmineralised osteoid at sites of stress (e.g., femoral neck, pubic rami, scapula).
Demographics
- Groups:
- Elderly/Institutionalised: Lack of sunlight.
- Asian/Afro-Caribbean: Darker skin reduces UV conversion of Vit D.
- Malabsorption: Coeliac, Crohn's, Gastric Bypass.
- Diet: Vegans (low dietary Ca/Vit D).
Mechanism
- Deficiency: Low Vitamin D -> Reduced intestinal absorption of Calcium and Phosphate.
- Compensation: Low Calcium triggers Parathyroid Hormone (PTH) release (Secondary Hyperparathyroidism).
- Correction: PTH restores serum Calcium by:
- Pulling Calcium out of bones (Demineralisation).
- Increasing Renal Phosphate excretion (Phosphaturia).
- Result: Serum Calcium is maintained (usually), but Serum Phosphate falls.
- Soft Bones: The Calcium x Phosphate product is too low to mineralise osteoid. The osteoblasts keep working (High ALP) but lay down soft rubbery matrix instead of hard bone.
| Feature | Osteomalacia | Hyperparathyroidism (Primary) | Paget's Disease | Multiple Myeloma |
|---|---|---|---|---|
| Calcium | Low/Normal | High | Normal | High |
| Phosphate | Low | Low | Normal | High/Normal |
| ALP | High | High/Normal | Very High | Normal/High |
| PTH | High (Secondary) | High (Primary) | Normal | Suppressed |
Symptoms
Signs
Biochemistry (The Typical Profile)
- Vitamin D: Very Low (less than 25 nmol/L).
- Calcium: Low or Normal (PTH compensation).
- Phosphate: Low.
- ALP: Elevated (often markedly).
- PTH: Elevated (Secondary Hyperparathyroidism).
Radiology
- X-Ray:
- Looser's Zones (Pseudofractures).
- Codfish Vertebrae: Biconcave indentation of endplates.
- Triradiate Pelvis: In severe, longstanding cases.
- Bone Biopsy (Rarely needed): Shows wide osteoid seams.
Management Algorithm
DIAGNOSED OSTEOMALACIA
(Low Vit D, High ALP)
↓
ASSESS KIDNEY FUNCTION
┌─────────┴─────────┐
NORMAL CKD (eGFR less than 30)
↓ ↓
STANDARD LOADING SPECIALIST CARE
REGIMEN (Needs Alfacalcidol)
↓
LOADING DOSE (Rapid Correction)
• **Colecalciferol** (Vit D3)
• Regime: 50,000 IU weekly for 6 weeks
(Total ~300,000 IU)
↓
MAINTENANCE DOSE (Lifelong)
• 800-2,000 IU Daily
• Consider Calcium supplements if
dietary intake less than 700mg/day
↓
MONITORING
• Check Ca at 1 month (rule out Primary Hyperpara)
• ALP takes 3-6 months to normalize
Therapeutics
- Colecalciferol (Vitamin D3): The standard treatment.
- Oral: Preferred.
- IM: If compliance or malabsorption is an issue.
- Calcium: Only needed if dietary intake is poor. Vitamin D increases absorption of dietary calcium efficiently.
- Alfacalcidol (1-alpha-hydroxy Vit D): Used ONLY in Renal Failure. Since the kidney cannot activate Colecalciferol, the active form must be given.
- Factures: Hip, pelvis, wrist.
- Deformity: Kyphosis, pelvic deformity (obstructed labour risk).
- Hypocalcaemia: Tetany (rare, as PTH compensates well).
- Excellent: Full recovery of bone strength and muscle power with treatment, though it takes 3-6 months.
- Pain: Often resolves within weeks.
Key Guidelines
| Guideline | Organisation | Key Recommendations |
|---|---|---|
| Vitamin D | NOS/ROS (2018) | Protocols for loading and maintenance doses. |
| Osteomalacia | ECTS | Clinical management of adult rickts. |
Landmark Evidence
1. Francis et al (NOS Guideline 2013)
- Established the standard UK loading regimen of ~300,000 IU over 6-10 weeks. This rapidly refills stores without causing toxicity.
What is Osteomalacia?
It means "soft bones". Bones are made of a protein mesh (collagen) filled with concrete (calcium). In this condition, you have plenty of mesh but not enough concrete. The bones become rubbery and bendy, which causes deep aching pain.
Is it the same as Osteoporosis?
No. Osteoporosis is "brittle bones" where you have less bone overall, but the bone you have is normal. Osteoporosis doesn't hurt until you break something. Osteomalacia hurts all the time.
Why do I have it?
The most common cause is lack of Vitamin D (from sunlight or diet), which is needed to absorb calcium from your food.
Will I recover?
Yes. It is completely curable. We give you high doses of Vitamin D for a few weeks to "fill up the tank", then a lower dose to keep you topped up. Your bones will harden up, and the pain and muscle weakness will go away, but it can take a few months.
Primary Sources
- Francis RM, et al. Vitamin D and Bone Health: A Practical Clinical Guideline for Patient Management. National Osteoporosis Society. 2013.
- Munns CF, et al. Global Consensus Recommendations on Prevention and Management of Nutritional Rickets. J Clin Endocrinol Metab. 2016.
- Bhan A, et al. Adult Rickets and Osteomalacia. Curr Osteoporos Rep. 2010.
Common Exam Questions
- Diagnosis: "Bone pain + Proximal weakness + High ALP?"
- Answer: Osteomalacia.
- Radiology: "Looser's Zones?"
- Answer: Pseudofractures (Osteomalacia).
- Biochemistry: "Calcium Low, Phosphate Low, ALP High?"
- Answer: Vit D Deficiency / Osteomalacia.
- Renal: "Treatment for renal osteodystrophy?"
- Answer: Alfacalcidol (Activated Vit D).
Viva Points
- Why is ALP High?: Osteoblasts require an alkaline environment to lay down bone. They differntiate and become overactive trying to repair the unmineralised bone, leaking ALP into the blood.
- Proximal Myopathy: Always test for this (ask patient to stand from chair without arms). It is the most specific clinical sign distinguishing it from simple bone pain.
Medical Disclaimer: MedVellum content is for educational purposes and clinical reference. Clinical decisions should account for individual patient circumstances. Always consult appropriate specialists.